On the efficacy of electrocatalysis in nonaqueous Li-O2 batteries

Heterogeneous electrocatalysis has become a focal point in rechargeable Li-air battery research to reduce overpotentials in both the oxygen reduction (discharge) and especially oxygen evolution (charge) reactions. In this study, we show that past reports of traditional cathode electrocatalysis in nonaqueous Li-O(2) batteries were indeed true, but that gas evolution related to electrolyte solvent decomposition was the dominant process being catalyzed. In dimethoxyethane, where Li(2)O(2) formation is the dominant product of the electrochemistry, no catalytic activity (compared to pure carbon) is observed using the same (Au, Pt, MnO(2)) nanoparticles. Nevertheless, the onset potential of oxygen evolution is only slightly higher than the open circuit potential of the cell, indicating conventional oxygen evolution electrocatalysis may be unnecessary.     

CO2-adsorbent spongy electrode for non-aqueous Li–O2 batteries

Regulation of the Li₂CO₃ byproduct is the most critical challenge in the field of non-aqueous Li–O₂ batteries.Although considerable efforts have been devoted to preventing Li₂CO₃ formation,no approaches have suggested the ultimate solution of utilizing the clean Li₂O₂ reaction instead of that of Li₂CO₃.Even if extremely pure O₂ is used in a Li–O₂ cell,its complete elimination is impossible,eventually generating CO₂ gas during charge.In this paper,we present the new concept of a CO₂-adsorbent spongy electrode(CASE),which is designed to trap the evolved CO₂ using adsorption materials.Various candidates composed of amine functional groups(–NH2)for capturing CO₂ were screened,with quadrapurebenzylamine(QPBZA)exhibiting superior CO₂-adsorbing ability among the proposed candidates.Accordingly,we fabricated the CASE by sandwiching QPBZA between porous carbon layers,which facilitated the transport of gaseous products.The new electrode was demonstrated to effectively capture the evolved CO₂ during charge,therefore altering the reaction pathways to the ideal case.It is highly advantageous to mitigate the undesirable CO₂ incorporation in the next discharge,resulting in improved cyclability.This novel concept of a CO₂-sponging electrode provides an alternative route to the realization of practically meaningful Li–O₂ batteries.     

Novel DMSO-based electrolyte for high performance rechargeable Li-O2 batteries

A dimethyl sulfoxide (DMSO) based electrolyte is first proposed for rechargeable lithium-O(2) (Li-O(2)) batteries. Superior battery performances, including high discharge capacity and low charge potential, are successfully obtained.     

Defective TiO2 hollow nanospheres as photo-electrocatalysts for photo-assisted Li-O2 batteries

The large overpotential for conventional Li-O₂ batteries is an enormous challenge, which impedes their practical application. Here, we prepare a defective TiO₂ (Ov-TiO₂) hollow nanosphere as photo-electrocatalyst for photo-assisted Li-O₂ batteries to reduce the overpotential. Under illumination, the oxygen vacancies as a charge separation center contribute to the separation of electrons and holes. The generated electrons could promote reducing O₂ to Li₂O₂ during oxygen reduction reaction (ORR) process, while the generated holes are beneficial to Li₂O₂ decomposition during oxygen evolution reaction (OER) process. Additionally, the proper concentration of oxygen vacancies will decrease the recombination rate between electrons and holes. The photo-assisted Li-O₂ batteries with Ov-TiO₂-650 exhibit advanced performances, such as the low overpotential (0.70 V), the fine rate capability, and the considerable reversibility accompanied with the formation/decomposition of Li₂O₂. We expect that these results could open a new mind to design of highly efficient photo-electrocatalysts for photo-assisted Li-O₂ battery.     

多孔Fe_2O_3纳米纤维用于高容量长寿命锂空气电池催化剂

采用静电纺丝技术,以乙酰丙酮铁[Fe(C5H7O2)3]、聚乙烯吡咯烷酮(PVP)和二甲基甲酰胺(DMF)为原料,制备了由Fe2O3纳米颗粒组成的高比表面积的多孔纳米纤维,并成功应用于锂氧气电池用催化剂.Fe2O3纳米颗粒为反应提供了充足的活性位点,提高了电池容量;而三维网状结构为反应物及产物提供了足够的反应及储存空间,避免了对电极孔道堵塞的问题,从而达到了锂空气电池长循环的目的.     

Recent advances in charge mechanism of noble metal-based cathodes for Li-O2 batteries

Lithium-oxygen(Li-O₂ ) batteries are considered as the next generation for energy storages systems due to the higher theoretical energy density than that of Li-ion batteries. However, the high charge overpotential caused by the insulated Li₂O₂ results in low energy efficiency, side reaction from electrolyte and cathode, and therefore poor battery performance. Designing noble metal-based catalysts can be an effective strategy to develop high-performance Li-O_2...     

Enhanced electrocatalytic performance of Fe-TiO2/N-doped graphene cathodes for rechargeable Li-O2 batteries

Journal of Solid State Electrochemistry - The Fe3+-doped TiO2 on nitrogen-doped graphene (Fe-TiO2/N-doped graphene) electrocatalyst is synthesized and employed as cathode material for Li-O2...     

Enhanced cyclability of sulfur cathodes in lithium-sulfur batteries with Na-alginate as a binder

Na-alginate as a binder in an aqueous solvent has been applied in the preparation of sulfur cathodes for lithium-sulfur batteries.Their electrochemical performances have been investigated by a charge-discharge cycle test and electrochemical impedance spectroscopy (EIS).The EIS tests indicated that the alginate sulfur cathode had lower resistance and better kinetic characteristics than those of the poly (vinylidene fluoride) (PVDF) sulfur cathode using PVDF as a binder in a N-methy-2-pyrrolidone (NMP) solvent.The charge-discharge tests showed that the discharge capacity and the capacity retention rate of Na-alginate sulfur cathode were 508 mAh·g-1and 65.4% at the 50th cycle with a current density of 335 mA·g-1.Compared with PVDF sulfur cathode,the alginate sulfur cathode showed a remarkably better cycle performance.These results show that the alginate binder has promising potential for lithium-sulfur battery applications.     

Waxberry-like hierarchical NiCo2O4-decorated carbon microspheres as efficient catalyst for Li-O2 batteries

Journal of Solid State Electrochemistry - Rechargeable Li-O2 batteries have aroused wide concern due to the theoretically high value for specific energy density. However, exploring suitable...     

Screening for superoxide reactivity in Li-O2 batteries: effect on Li2O2/LiOH crystallization

Unraveling the fundamentals of Li-O(2) battery chemistry is crucial to develop practical cells with energy densities that could approach their high theoretical values. We report here a straightforward chemical approach that probes the outcome of the superoxide O(2)(-), thought to initiate the electrochemical processes in the cell. We show that this serves as a good measure of electrolyte and binder stability. Superoxide readily dehydrofluorinates polyvinylidene to give byproducts that react with catalysts to produce LiOH. The Li(2)O(2) product morphology is a function of these factors and can affect Li-O(2) cell performance. This methodology is widely applicable as a probe of other potential cell components.     

Amorphous CoSnO3@rGO nanocomposite as an efficient cathode catalyst for long-life Li-O2 batteries

An amorphous CoSnO₃@rGO nanocomposite fabricated using a surfactant-assisted assembly method combined with thermal treatment served as a catalyst for non-aqueous lithium-oxygen (Li-O₂) batteries. In contrast to the specific surface area of the bare CoSnO₃ nanoboxes (104.3 m² g^–1), the specific surface area of the CoSnO₃@rGO nanocomposite increased to approximately 195.8 m² g^–1 and the electronic conductivity also improved. The increased specific surface area provided more space for the deposition of Li₂O₂, while the improved electronic conductivity accelerated the decomposition of Li₂O₂. Compared to bare CoSnO₃, the overpotential reduced by approximately 20 and 60 mV at current densities of 100 and 500 mA g^?1 when CoSnO₃@rGO was used as the catalyst. A Li-O₂ battery using a CoSnO₃@rGO nanocomposite as the cathode catalyst cycled indicated a superior cyclic stability of approximately 130 cycles at a current density of 200 mA g^–1 with a limited capacity of 1000 mAh g^–1, which is 25 cycles more than that of the bare amorphous CoSnO₃ nanoboxes.     

Li-O2 battery with a dimethylformamide electrolyte

Stability of the electrolyte toward reduced oxygen species generated at the cathode is a crucial challenge for the rechargeable nonaqueous Li-O(2) battery. Here, we investigate dimethylformamide as the basis of an electrolyte. Although reactions at the O(2) cathode on the first discharge-charge cycle are dominated by reversible Li(2)O(2) formation/decomposition, there is also electrolyte decomposition, which increases on cycling. The products of decomposition at the cathode on discharge are Li(2)O(2), Li(2)CO(3), HCO(2)Li, CH(3)CO(2)Li, NO, H(2)O, and CO(2). Li(2)CO(3) accumulates in the electrode with cycling. The stability of dimethylformamide toward reduced oxygen species is insufficient for its use in the rechargeable nonaqueous Li-O(2) battery.     

Enhancement of cyclability using recombination reaction of Cu for Sn2Fe nanocomposite anode for lithium-ion batteries

A Sn₂Fe/C nanocomposite containing Cu was evaluated as an anode material for rechargeable lithium-ion batteries. The electrochemical reaction mechanism of this nanocomposite was examined by ex-situ X-ray diffraction and high resolution transmission electron microscopy. The Sn₂Fe/C nanocomposite containing Cu showed dramatically improved cycling performance. The enhanced cyclability of the Sn₂Fe/C nanocomposite containing Cu was attributed to both amorphization of the Sn₂Fe phase and a recombination reaction between Sn and Cu during the charging step.     

Electrical conductivity in Li2O2 and its role in determining capacity limitations in non-aqueous Li-O2 batteries

Non-aqueous Li-air or Li-O(2) cells show considerable promise as a very high energy density battery couple. Such cells, however, show sudden death at capacities far below their theoretical capacity and this, among other problems, limits their practicality. In this paper, we show that this sudden death arises from limited charge transport through the growing Li(2)O(2) film to the Li(2)O(2)-electrolyte interface, and this limitation defines a critical film thickness, above which it is not possible to support electrochemistry at the Li(2)O(2)-electrolyte interface. We report both electrochemical experiments using a reversible internal redox couple and a first principles metal-insulator-metal charge transport model to probe the electrical conductivity through Li(2)O(2) films produced during Li-O(2) discharge. Both experiment and theory show a "sudden death" in charge transport when film thickness is ~5 to 10 nm. The theoretical model shows that this occurs when the tunneling current through the film can no longer support the electrochemical current. Thus, engineering charge transport through Li(2)O(2) is a serious challenge if Li-O(2) batteries are ever to reach their potential.     

Graphene sheet-encased silica/sulfur composite cathode for improved cyclability of lithium-sulfur batteries

Journal of Solid State Electrochemistry - The “shuttle effect” of polysulfides is a serious issue, resulting in a decrease in the life-cycle of lithium-sulfur (Li-S) batteries. To...     

All-solid-state batteries with Li2O-Li2S-P2S5 glass electrolytes synthesized by two-step mechanical milling

Sulfide solid electrolytes, which show high ion conductivity, are anticipated for use as electrolyte materials for all-solid-state batteries. One drawback of sulfide solid electrolytes is their low chemical stability in air. They are hydrolyzed by moisture and generate H₂S gas. Substituting oxygen atoms for sulfur atoms in sulfide solid electrolytes is effective for suppression of H₂S gas generation in air. Especially, the xLi₂O·(75-x)Li₂S·25P₂S₅ (mol%) glasses hardly generated H₂S gas in air. However, substituting oxygen atoms for sulfur atoms caused a decrease in conductivity. The x?=?7 glass showed high chemical stability in air and maintained high conductivity of 2.5?×?10^?4 S cm^?1 at room temperature. Performance of cells using the 7Li₂O·68Li₂S·25P₂S₅ and the 75Li₂S·25P₂S₅ glasses as solid electrolytes were compared. All-solid-state C/LiCoO₂ cell using the 7Li₂O·68Li₂S·25P₂S₅ glass produced performance as good as that obtained using the 75Li₂S·25P₂S₅ glass. Capacity retention and change of interfacial resistance of the former cell were superior to those of the latter cell after storage at 4.0 V and 60 °C. The diffusion of oxygen element into the 7Li₂O·68Li₂S·25P₂S₅ glass was less than that into the 75Li₂S·25P₂S₅ glass after storage at the voltage of 4.0 V at 60 °C. Improvement of the stability of sulfide solid electrolytes to moisture was related to cell performance as well as an increase in conductivity.     

High capacity Na-storage and superior cyclability of nanocomposite Sb/C anode for Na-ion batteries

A Sb/C nanocomposite was synthesized and found to deliver a reversible 3 Na storage capacity of 610 mA h g(-1), a strong rate capability at a very high current of 2000 mA g(-1) and a long-term cycling stability with 94% capacity retention over 100 cycles, offering practical feasibility as a high capacity and cycling-stable anode for room temperature Na-ion batteries.